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Manuscript Title: An interactive simulation program for visualizing complex phenomena in solids.
Authors: J. Merimaa, L.F. Perondi, K. Kaski
Program title: Fracture
Catalogue identifier: ADKS_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 124(2000)60
Programming language: C.
Computer: DEC ALPHA 300.
Operating system: UNIX.
RAM: 2M words
Keywords: Lennard-jones, Molecular dynamics, Fracture, Crack dislocations, Solid state physics, Other.
Classification: 7.7.

Nature of problem:
In a typical research activity involving simulations of complex physical systems, one is often faced with a 'research loop', which may be loosely described as follows: definition of input data; running of a simulation, outputting data to a storage disk; post-processing of the accumulated data for extracting relevant information with the eventual aid of graphics and numerical packages; definition of new input parameters and, closing the loop, starting a new simulation run. Advances in computer hardware, mainly faster processors, and the increased availability of software development tools, with plenty of graphics resources, have been markedly increasing the feasibility of alternative solutions for improving the above scheme.

Solution method:
Interactive simulations offer an attractive option for the study of systems in which a great deal of feedback, in the sense described above, is required. They are also ideal for teaching purposes. The present program gives an illustration of an interactive simulation environment. The dynamical behaviour of a two-dimensional Lennard-Jones 'solid' under stress, with either a grain boundary or an initial crack, is simulated through a molecular dynamics algorithm.

The interactiveness concept strongly relies on the display of an animated graphical representation of the system. The quality of the animation depends on the rate with which frames are displayed on the graphical display window. This rate, in its turn, depends on the iteration time of the simulation algorithm. Hence, the size of the systems which may be investigated, while maintaining an acceptable animation quality, depends on the machine processor. Systems with up to 50,000 atoms give fair animations for the target machine given above. Subjecting the system to strain rates sufficiently high for inducing atomic displacements of the order of the mean inter-atomic distance in one integration step will cause the program to collapse. Studies at such high rates will require modifications of the MD algorithm. The implementation of an adaptative integration method will, most possibly, be enough for most applications.

Unusual features:
Although the program has been originally designed for illustrative purposes, its final version incorporates features which, we believe, render it in a good standard for research work in two-dimensional models, provided a better treatment is given to thermal effects. In particular, it has been endowed with a control which allows the user to generate an instantaneous 'snapshot' of the graphics screen. The image is stored in a bitmap file (X11 standard), created under the same directory in which the program is running. The graphical part relies on the MOTIF library.

Running time:
The typical running time is machine and system size dependent.